Design of a radial mode thermoacoustic prime mover (sound source) and experimental observations

Experimental thermoacoustics has been limited in the past to plane wave systems. Swift briefly discussed the radial mode thermoacoustic engine, but no working models have been built. Radial modes of a cylindrical resonator are naturally anharmonic; thus harmonic generation at high sound‐pressure levels by nonlinear processes tend to be less resonance enhanced in the radial mode, potentially leading to higher sound‐pressure levels in the fundamental radial mode of oscillation. A radial mode prime mover which is theoretically optimized for a 60% helium, 40% argon gas mixture (mole fraction) at atmospheric pressure has been constructed. Details of the design and construction, measurement of the power dissipated in the hot heat exchanger (required for onset of self oscillation) as a function of ambient pressure, and harmonic distortion of the fundamental mode of oscillation will be presented. [Work supported by ONR.]